DESCRIPTION: The specific goal of the proposed research is to expand the understanding of selenoprotein RNA metabolism in mammalian cells. However, the investigator's findings will likely apply to other nonsense-containing transcripts and lend important insight into the cis-acting sequences and trans-acting factors either promote or inhibit nonsense-mediated mRNA decay (NMD). The specific aims are to: 1. Achieve insight into the mechanism by which the premature termination of GPx1 mRNA translation at the position of the Sec codon mediates cytoplamic mRNA decay. 2. Determine why premature termination of PHGPx mRNA translation at the position of the Sec codon fails to mediate a significant reduction in PHGPx mRNA abundance.